1. Field of the Invention
The present invention relates to a data transmission system for performing transmission/reception of data in accordance with a predetermined transmission protocol between the card reader/writer of a terminal device and an IC card connected to the card reader/writer.
2. Description of the Related Art
In recent years, as a portable data storing/processing medium used in various applications, an IC card incorporating an IC chip having a nonvolatile data memory and a control element such as a CPU for controlling the data memory has received a great deal of attention.
The IC card of this type is generally inserted into a terminal device and connected to the terminal device through a card reader/writer arranged in the terminal device, thereby performing a predetermined function such as a transaction function. This application function is generally initialized such that command data is sent from the terminal device to the IC card. The IC card generally operates as follows. The IC card receives the command data from the terminal device through the card reader/writer, decodes a function code included in the command data, performs processing corresponding to the function code, and then returns data representing the processing result as response data to the terminal device through the card reader/writer.
In this case, the IC card generally performs transmission/reception of data with the card reader/writer in accordance with a transmission protocol which is a data transmission standard defined in the known ISO/IEC 7816-3 standard rule.
At this time, when the IC card supports a plurality of different transmission protocols, i.e., when the IC card has a plurality of protocols corresponding to a plurality of application systems for service or transaction performed using the IC card, the IC card can be commonly used in the plurality of applications by switching only the transmission protocols. In other words, the IC card can be commonly applied to these systems.
In such a data transmission system, such as that known in the prior art such as Japanese Patent Application (KOKAI) Publication No.4-321192, when a plurality of transmission protocols are switched in accordance with an application purpose, a method called a PTS (Protocol Type Selection) method is defined in the ISO/IEC 7816-3 standard. According to the PTS method, when a plurality of transmission protocols are supported in one IC card, a transmission protocol to be used as a default protocol is always determined in an initial state. Therefore, when a transmission protocol other than the default protocol is to be used in the IC card, the PTS method must be used, and a transmission protocol to be used must be selected from the plurality of supported protocols.
As a method of selecting a transmission protocol to be used, the following method is considered. Priority information for a plurality of transmission protocols is stored in a nonvolatile memory (e.g., EEPROM) in the IC card, and this priority information is rewritten by a special command to set the transmission protocol used in the IC card itself to have the first priority, so that this transmission protocol is always used as a default protocol.
However, in order to use the above techniques, the same conditions for transmitting/receiving the command for performing the PTS method or the special command for changing the priority are used in the application systems. In particular, when the data transmission rates of the systems are different from each other, these techniques cannot be used.